Fluorescent lamp cathode and method of making cathodes

Abstract

A method of making cathodes includes forming a first intermediate assembly having a current wire in juxtaposition with an outer mandrel wire and a basket wire wound around the first two wires. The first intermediate assembly is wound around a central mandrel to form a second intermediate assembly. Pulses of energy are used to produce an alloy solder joint between the current wire and the basket wire at selected locations. The second intermediate assembly is cut into segments, and the mandrels are removed. This results in a cathode having a coiled current wire and a basket wire wound around the current wire, with the basket wire being bonded to the current wire by the alloy solder joints. The cathode includes a central bore that is substantially free of the alloy solder joint.

1. A method of making a cathode comprising:
 placing a current wire in juxtaposition with an outer mandrel wire; 
 winding a basket wire around said juxtaposed current wire and outer mandrel wire to form a first intermediate assembly; 
 winding said first intermediate assembly around a central mandrel to form a second intermediate assembly; 
 subjecting selected locations on said second intermediate assembly with pulses of energy so as to partially melt said current wire, said basket wire and said outer mandrel wire and produce an alloy solder joint between said current wire and said basket wire at said selected locations 
 cutting said second intermediate assembly into a number of segments; and 
 removing said outer mandrel wire and said central mandrel from each segment, thereby defining an open-ended central bore in each segment that is substantially free of said alloy solder joint. 
 
     
     
       2. The method of  claim 1  wherein said pulses of energy are laser beams. 
     
     
       3. The method of  claim 1  wherein said pulses of energy cause little or no melting of said central mandrel. 
     
     
       4. The method of  claim 1  wherein said second intermediate assembly is moved continuously while subjecting said second intermediate assembly to said pulses of energy. 
     
     
       5. The method of  claim 1  wherein said selected locations are spaced apart at a uniform distance that is equal to a desired length for said cathode. 
     
     
       6. The method of  claim 5  wherein said second intermediate assembly is cut at said selected locations. 
     
     
       7. The method of  claim 1  wherein said outer mandrel wire and said central mandrel are removed by being chemically dissolved. 
     
     
       8. The method of  claim 1  wherein said current wire and said basket wire are made of tungsten and said outer mandrel wire and said central mandrel are made of steel. 
     
     
       9. The method of  claim 1  wherein each pulse of energy has a duration of about 4-6 milliseconds and a total power of about 7-15 joules. 
     
     
       10. A cathode comprising:
 a coiled current wire; and 
 a basket wire wound around said current wire, said basket wire being bonded to said current wire at one or more locations by an alloy solder joint between said current wire and said basket wire; 
 wherein said current wire and said basket wire are configured to define a central bore that extends the entire length of said cathode and is substantially free of said alloy solder joint. 
 
     
     
       11. The cathode of  claim 10  wherein said current wire and said basket wire are made of tungsten. 
     
     
       12. The cathode of  claim 11  wherein each alloy solder joint comprises a tungsten-iron alloy. 
     
     
       13. The cathode of  claim 10  wherein said basket wire is bonded to said current wire by an alloy solder joint at each end of said cathode. 
     
     
       14. The cathode of  claim 13  wherein said alloy solder joints do not extend across said ends of said cathode.